Multi Regime combustion under technically relevant conditions: Experimental and numerical investigation of thermo-chemical states and flame structures

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Turbulent combustion can be classified as premixed or non-premixed. These two limiting cases have been studied extensively and mathematical models have been developed for premixed and non-premixed flames. Besides these two limits, stratified and partially premixed flames have also been investigated, using however either premixed or non-premixed models. Modeling of flames, which can neither be categorized as premixed nor as non-premixed (multi regime combustion), is an open scientific issue. Multi regime combustion can be found in a variety of practical systems such as gas turbines or engines.Recent studies have shown that the local flame structures in multi regime combustion can differ significantly from both limiting cases. Currently, no suitable LES model exists that is capable of describing both the premixed/non-premixed limits as well as the intermediate states. Furthermore, no experimental reference data set is available, where the different flame structures are realized through systematic variations of boundary conditions. Therefore, the objective of this study is a systematic experimental and numerical investigation, model development and analysis of multi regime combustion.The research project consists of 3 work packages (AP). In the experimental work package AP1 a burner with well-defined boundary conditions for generating the reference data will be developed. Flame stabilization is achieved through recirculation zones such that the combustion regime can be controlled by varying the inlet conditions both in velocity and stoichiometry. The cold flow and mixture field will be characterized with high-speed PIV and Raman spectroscopy. For the combusting cases, the thermo-chemical state will be recorded with Raman/Rayleigh scattering. Furthermore, simultaneous quantitative OH-LIF measurements will be carried out for the first time.In the numerical AP2 two-dimensional flamelet equations (mixture fraction and progress variable formulation) will be solved. For a subsequent usage in LES and for comparison with the experiments a novel parameterization will be developed based on additional progress variables instead of scalar dissipation rates. Initially, the model will be tested against fully resolved solutions of a triple flame. For the LES flamelet tables, statistical information from experimentally determined joint probability density functions will be analyzed and integrated.In AP3 experimental and numerical methods will be combined. As a first step the results from the LES will be validated. Subsequently, the identification of combustion regimes, the characterization of the local thermo-chemical state and the flame structure will be carried out. This analysis will be based on a novel gradient-free flame identification and flame characterization method developed in this project. The project will be carried out in close collaboration with Prof. Vervisch as Mercator fellow.